Certain video disc records and player systems have been designed for storing and recovering television signals comprising composite video and accompanying sound signals. The sound signals are recorded in monophonic or one channel format. The monophonic audio signal is recorded with a relatively wide signal bandwidth with respect to signal noise considerations since typical television receiver audio circuits have limited bandwidth and tend to remove the high frequency noise. Subsequent players and record discs were designed to accommodate stereophonic sound signals. The stereophonic audio signals are recorded with a higher signal-to-noise ratio and a narrower noise bandwidth in contemplation of these signals being reproduced via high quality, wide band audio amplifiers separate from the television receiver. In order to provide backward compatibility of the later designed records with the former players, the stereophonic or stereo sound signals were matrixed onto two channels, such that the conventional left plus right (L+R) stereo signal is recorded on a first sound channel and the conventional left minus right (L-R) stereo signal is recorded on a second sound channel. The first sound channel in the stereo system is made substantially equivalent to the single sound channel in the monophonic system and therefore the stereo records are configured to be played on the monophonic player. In addition, the matrix (decoding) circuitry in the stereo player, for separating the left and right signals from the matrixed signals in the first and second sound channels, is designed to reproduce monophonic sound signals recovered from a monophonic video disc record by the stereo player.
In order to enhance sound quality further in the later stereo systems, the stereo components of the sound signals were compressed prior to recording, to preserve the effective dynamic range of the signal and to reduce noise content. The stereo video disc player therefore necessarily includes expander circuitry to restore the signal to normal form. The system remains backward compatible since compressed signals reproduced without expansion are not objectionable. However, expansion of the uncompressed monophonic signal, by the stereo player playing a monophonic video disc wherein no provision has been made for audio noise reduction, may result in objectionable sound quality.